An inflatable packer is a normally retracted device that is expanded into sealing engagement with a well conduit wall by pumping fluid under pressure into the interior of the packer unit. The packer unit comprises an inner elastomer bladder that is covered on its outside by a reinforcement such as an extrusion barrier for the bladder. When inflation pressure is relieved, the bladder and reinforcements retract toward their original size.
Unless the shape of the bladder is controlled during expansion, it can experience Z-folding, particularly when the packer has a high expansion ratio, which is the ratio being its fully expanded and fully retracted outer diameters. Generally an expansion ratio greater than 2:1 is considered to be high. Where the ratio is high, the bladder can initially inflate with a bubble so that it does not conform to the reinforcement. As a result, what can be called a Z-fold in the bladder is formed where a portion is folded back upon itself. Such folding causes high axial strains in the bladder and decreases the expanded thickness thereof. Generally, Z-folding occurs during inflation if the energy for the elastomer bladder to continue radial expansion is greater than the energy for the bladder to extend axially over an uninflated portion of the bladder. It has been found that bladders in slat-style packers are particularly susceptible to Z-folding problems under long lengths of exposed metal slats.
A general object of the present invention is to provide a new and improved inflatable packer having means to control bladder shape during inflation.
Another object of the present invention is to provide a new and improved inflatable packer including means to control bladder shape and thereby prevent severe folding of the bladder which can cause axial strains.
Still another object of the present invention is to provide a new and improved inflatable packer where the bladder unit has increased axial stiffness relative to its hoop or circumferential stiffness in order to control the shape thereof during expansion.